Clemens, in U.S. Pat. Nos. 3,842,194, 3,842,217 and 3,909,517, has described a conductive video disc comprising a molded plastic disc having audio, video and color information in the form of geometric variations in a spiral groove in the disc surface. These discs were then coated first with a conductive material such as a metal layer which acts as a first electrode, and then with a dielectric layer, such as an inert polymer layer. A metal tipped stylus acts as a second electrode of a capacitor and the information signals are monitored by the stylus which notes changes in capacitance between the stylus and the disc surface as the information, in the form of depressions, passes beneath the stylus when relative motion is established between the disc and the stylus.
In order to prevent undue wear between the disc and the stylus, a lubricant layer was also applied to the disc surface by evaporation. Suitable lubricants were found to be compounds of the formula ##STR2## wherein R is an alkyl group of 4-20 carbon atoms and n is an integer, as disclosed by Matthies in U.S. Pat. No. 3,833,408.
Further developments in this system have produced a video disc which is made of a conductive plastic material, e.g., a polyvinylchloride polymer resin containing sufficient amounts of conductive particles, such as conductive carbon particles, so that the disc can provide capacitance readout. The carbon particles are surrounded by organic materials such as the plastic resin and various processing additives which provide a dielectric surface layer on the conductive particles. This development has eliminated the need for separate coatings of metal and dielectric on the plastic disc, and thus has greatly improved the economics of the system. In other developments, video discs which do not require a grooved surface are also under development. The stylus is maintained in synchronization with the information pattern by means of electrical signals on either side of the information track, rather than physically by means of the groove walls.
The stylus, formerly made of metallized sapphire, has also been improved so that metallized diamond can be employed. Diamond is a harder, longer wearing material than sapphire and is thus preferred. However, a diamond stylus also requires good lubrication of the disc surface.
These changes in materials led to the need for a modification of the lubricant whereby lubricants included in the general formula above, but limited as to molecular weight and purity, were needed. Copending application of Wang et al, Ser. No. 937,819, filed Aug. 29, 1978, discloses the use of methylalkylsiloxanes of the formula ##STR3## wherein R.sub.1 and R.sub.2 are alkyl groups of 4-20 carbon atoms, x is an integer of 2-4 and y is an integer of 0-2 and wherein the sum of x and y is 4 or less, as improved video disc lubricants for conductive carbon loaded video discs. The modified methylalkylsiloxanes can be readily applied to the video disc, as by spraying which is the preferred application method, and give improved results as lubricants. However, these materials have the disadvantage that they are rather expensive to prepare, requiring several processing steps including molecular distillation under high vacuum conditions, also entailing the need for expensive equipment. Thus it would be desirable to obtain another lubricant that can meet the stringent requirements for the video disc and be simpler and less expensive to manufacture.